Reyes' sacrifice fly in the third inning cut into a 2-0 Brewers lead. Then in the next frame, the Marlins erupted for four runs, sending 10 men to the plate.
After scoring on singles by Donnie Murphy and Donovan Solano and on an error by Milwaukee pitcher Mike Fiers, Reyes completed the uprising with a two-run hit, giving the Marlins a 6-2 advantage.
Ricky Nolasco (11-12) earned the victory, allowing three runs (one earned) on nine hits in a seven-inning effort. The right-hander didn't issue a walk and struck out four.
Steve Cishek got the game's final out for his 12th save as the Marlins took the opener of a four-game series.
Fiers (8-7) was tagged for six runs (four earned) on six hits over 3 1/2 frames.
Carlos Gomez socked a two-run homer for Milwaukee.